A pressure sensor including a semiconductor substrate and a glass pedestal is described in JP-A-2-69630 or JP-A-4-114478, for example. The semiconductor substrate includes a thin diaphragm for detecting a pressure, and a thick wall portion around the diaphragm. One side surface of the glass pedestal is bonded to the thick wall portion of the semiconductor substrate. Furthermore, a through hole is provided in the glass pedestal to penetrate through from the one side surface of the glass pedestal to the other side surface thereof, so that a pressure is introduced to the diaphragm through the through hole from an opening on the other surface of the glass pedestal.
However, in this pressure sensor, if the through hole of the glass pedestal is large, foreign materials such as dust are easily introduced into the through hole due to the pressure. If the foreign materials adhere on the diaphragm, sensor characteristics of the pressure sensor will be changed.